In a prior known hub odometer, the balls are positioned above and the counting mechanism is positioned below the axis of rotation of the case. A rotor is provided in the case and balls are movable in a chamber on the rotor substantially only radially with respect to the axis of rotation of the case. The horizontal position of the counting mechanism mounted on the rotor during the rotation of the case is ensured as the center of gravity of the rotor is below the axis of rotation of the case. On the backside of the rotor base a stepping mechanism is positioned, which is driven through a slotted crank by an eccentric disk rotating together with the case about the axis of rotation of the case. Coupling between the disc and counting mechanism consists of a worm gear mounted on the front side of the rotor base. Although this results in a relatively thin construction of the odometer in the direction of the axis of rotation of the case, the axial thickness of the odometer is still relatively great due to the construction of the reduction gear. Furthermore, the rotor requires a relatively great amount of material, in order to provide a counter weight for the balls positioned above the axis of rotation of the case, which counter weight ensures that the weight of the balls does not cause a rotation of the carrier and consequently a reversal of the counting mechanism in its position of rest.
In another known odometer as disclosed in U.S. Pat. No. 3,130,907, seven balls are positioned in a plane behind the counting mechanism within an annular space completely surrounding the axis of rotation of the case. With this construction most of the balls as well as the counting mechanism lie below the axis of rotation of the case in the position of rest, in order to ensure that the center of gravity of the carrier and its built-in parts are as far as possible below this axis of rotation. This construction results in an extremely great axial thickness of the odometer.